The present invention relates to a wet image forming apparatus applicable as an electrophotographic copying machine or a laser beam printer and using a developing solution in which toner is dispersed in a solvent.
A liquid developer used in this type of wet image forming apparatus mainly comprises a petroleum nonpolar solvent and toner particles made of resin and pigment dispersed in the solvent. A charge assisting agent is added to the solvent liquid, and the toner is charged at a predetermined potential by means of the charge assisting agent.
Since the toner particles used in the wet image forming apparatus have smaller diameters as compared to those used in a dry image forming apparatus, the image quality can be improved. In addition, since the resin content of the toner is low, less energy is required for fixation. For these reasons, the wet image forming apparatus has lately attracted considerable attention.
Incidentally, after development, the surplus developer which remains on a photosensitive body is lightly squeezed. After the squeeze, a toner image is sent to a transfer region, and transferred to a paper sheet by an electric field transfer method. In other words, an electric field is applied to the photosensitive body in the toner image transfer process, with the result that the toner is electrically migrated and transferred to the paper sheet.
The electric field transfer method has problems that a toner image is liable to be disturbed in the transfer process, and that the surplus solvent is transferred to the paper sheet and cannot be fully collected.
To solve the problems, an offset transfer method has been developed, in which a toner image is transferred by means of either heat or pressure or both heat and pressure in the transfer process without using cataphoresis.
According to the offset transfer method, since the toner image is completely dried before transfer, it is not disturbed in the transfer process. In addition, since the solvent, which is stinking and flammable, can be collected in an early part of the image forming process, the method is advantageous over the electric field transfer method.
In the offset transfer method, it is necessary to completely dry the toner image on the photosensitive drum during a period between development and transfer. For this purpose, generally, a squeeze roller is used together with a drying blower.
The squeeze roller is formed by, for example, die-moldering conductive polyurethane resin.
However, conventionally, when the surface configuration of the squeeze roller is determined, the relationship with the toner image formed on the photosensitive body or the relationship with the width of a portion where the squeeze roller contacts to the photosensitive body was not taken into consideration at all. Therefore, when the surplus developer is squeezed, an asperity pattern on the surface of the squeeze roller is stamped on the toner layer formed on the photosensitive drum. As a result, the quality of the toner image transferred from the photosensitive body to the paper sheet is lowered.
The present invention was made in consideration of the above matters. Accordingly, an object of the present invention is to provide a wet image forming apparatus, in which the surface of removing means has such a configuration as to be in contact with a developer image formed on an image carrier body with a uniform contact pressure and the height of a surface asperity of the removing means is lower than the thickness of the layer of the developer image on the image carrier body, so that the developer image formed on the image carrier body is prevented from disturbance when a surplus developer liquid is removed by the removing means.
An image forming apparatus of the present invention comprises: image forming means for forming a latent image on an image carrier body which is rotating; developing means, containing liquid developer in which developer particles are dispersed in a solvent, for supplying the liquid developer to the latent image on the image carrier body and forming a developer image; removing means, which rotates in contact with the image carrier body, for removing a surplus of the liquid developer remaining on the image carrier body after development; and transfer means for transferring the developer image to a transfer material after the surplus of the liquid developer is removed by the removing means, the removing means having a surface configuration which allows contact with the developer image on the image carrier body with a uniform contact pressure in a contact portion where the removing means contacts to the image carrier body.
An image forming apparatus of the present invention comprises: image forming means for forming a latent image on an image carrier body which is rotating; developing means, containing liquid developer in which developer particles are dispersed in a solvent, for supplying the liquid developer to the latent image on the image carrier body and forming a developer image; removing means, which rotates in contact with the image carrier body, for removing a surplus of the liquid developer remaining on the image carrier body after development; and transfer means for transferring the developer image to a transfer material after the surplus of the liquid developer is removed by the removing means, the removing means having surface roughness smaller than a thickness of a layer of the developer image formed on the image carrier body.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.